Diaper rash is a common form of irritation and inflammation of those parts of an infant's body normally covered by a diaper. This condition is also referred to as diaper dermatitis, napkin dermatitis, napkin rash, and nappy rash. While certainly more common in infants, this condition is not, in fact, limited to infants. Any individual who suffers from incontinence to the extent that the use of absorbent articles is required may develop this condition. This ranges from newborns, to the elderly, to critically ill or nonambulatory individuals.
It is generally accepted that true "diaper rash" or "diaper dermatitis" is a condition which is, in its most simple stages, a contact irritant dermatitis. The irritation of simple diaper rash results from extended contact of the skin with urine, or feces, or both. Diapers are worn to catch and hold the body waste, but generally hold the waste in direct contact with the skin until changed, i.e., in occluded fashion for long periods of time. The same is true for an incontinence pad, or incontinence brief. However, while it is known that the body waste "causes" diaper rash, the precise component or components of the urine or feces which are responsible for the resulting irritation of the skin have not been conclusively identified. The most commonly accepted list of factors linked to diaper rash includes ammonia, bacteria, the products of bacterial action, urine pH, Candida albicans, and moisture. These are generally cited in the art as being the most likely candidates for agents or conditions which produce or aggravate diaper rash.
As discussed in Berg and Stewart, U.S. Pat. No. 4,685,909, Issued Aug. 11, 1987, a primary cause of diaper rash appears to be a particular set of conditions which arises as a result of prolonged contact of skin with mixtures of feces and urine. Activity of proteolytic and lipolytic fecal enzymes, as well as fecal bacteria, present in such a mixture is believed to be a major factor in producing skin irritation. Urine in contact with enzymes and bacteria from feces can also result in production of ammonia which raises skin pH (and causes odor). This rise in skin pH, for example to levels of 6.0 and above, in turn increases that fecal proteolytic and lipolytic enzymatic activity which produces diaper rash. Urine itself can also contribute to diaper rash by adding moisture to the diaper environment. Water, and particularly water in the form of urine, is especially effective at diminishing the barrier property of skin, thereby enhancing the susceptibility of skin to fecal enzyme irritation. However, when skin pH is kept between about 3.0 and 5.5, the skin's barrier properties can be maintained. The foregoing diaper rash model suggests that effective diaper rash control can be achieved by maintaining skin pH well within the acidic range to inhibit irritation-producing enzymatic activity while simultaneously maintaining the diaper environment as dry as possible.
One factor in preventing a rise in skin pH to within the alkaline range involves the maintenance of aqueous fluids, e.g., urine, feces and/or mixtures thereof, discharged into and held within the diaper or incontinence article at an acidic pH. This can be accomplished by taking steps to inhibit ammonia formation in the article, by donating protons to the discharged liquids held within the absorbent article or by a combination of these methods. A number of prior art references, in fact, teach the addition of various acidic pH control or "ammonia-absorbing" agents to absorbent articles such as diapers, and agents of this type do tend to inhibit the rise of pH of aqueous fluids in the diaper. References with such disclosures include, for example, Alonso et al, U.S. Pat. No. 4,382,919, Issued May 10, 1983; Blaney, U.S. Pat. No. 3,964,486, Issued June 22, 1976; Bryce, U.S. Pat. No. 3,707,148, Issued Dec. 26, 1972; and Jones, Sr., U.S. Pat. No. 3,794,034, Issued Feb. 26, 1974.
One type of pH control agent or "buffering agent" frequently found in disposable absorbent articles comprises the slightly cross-linked polymeric gelling agents or "supersorbers" which serve to imbibe liquids discharged into the article. These materials frequently contain at least some unneutralized carboxylic acid or sulfonic acid groups in the polymer chain, and these acid groups can donate protons to fluid within the article. Polymeric gelling agents of this type are thus especially desirable components of the absorbent articles since they not only improve the absorbency characteristics of the article but they also provide at least some acid buffering capacity with respect to fluids in the article.
Whether the acidic pH control agent is of the polymeric gelling agent type or not, pH control agents alone will frequently not be able to provide sufficient buffering capacity to prevent a rise in the pH of urine or other discharged fluids within the absorbent article. This is because the amount of urine discharged into the typical absorbent article is often greater than the buffering capacity of the pH control agent can handle. Another factor which works against the action of an acidic buffering agent in inhibiting urine pH rise involves the presence of inorganic contaminants in the urine. Human urine, for example, frequently will contain bicarbonate salts which, after the urine is discharged, can decompose to produce CO.sub.2. CO.sub.2 dissipation from voided urine in turn tends to promote a rise in urine pH which can overcome whatever acid buffering capacity might be provided by the acidic pH control agent.
The foregoing considerations involving diaper rash, ammonia production and the importance of pH control of fluids within the absorbent article indicate that there is a continuing need to identify absorbent articles and components thereof which are especially effective for preventing the occurrence of conditions that favor the development of diaper rash and the production of odor-causing materials. Accordingly, it is an object of the present invention to provide disposable absorbent articles which are especially effective for reducing or preventing diaper rash and ammonia production. It is a further object of the invention herein to provide such absorbent articles which utilize readily available, non-toxic, non-irritating materials to provide the desired rash and odor combatting effectiveness. It is a further object of the present invention to provide absorbent articles of this type which can be prepared by relatively straightforward, conventional absorbent article production methods.